Stabilizer with condenser modulator



Jan. 30 ESQ 1... L. WEISGLASS 2,494,218

STABILIZER WITH CONDENSER MODULATOR Filed July 3, 1947 1 L5 LQJ/LmJ 5. WSIQ INVENTOR LOUIS L. WEISGLASS ATTORN EYS Patented Jan. 10, 1950 STABIEIZEB WITH CONDENSER MODULATOR Louis L. Weisglass, New York, N.

5 "assignor to ---Picker X-Ray Cdrporation Waite Manufacturing *DivisiomlIna, Cleveland,

Ohio, a corpora- This invention relates to X-ray systems and more particularly "to improved means for "maintaining the discharge current flowing-through the 'tube substantially constant by the use -of a co'ndenserin'the stabilizer circuit.

The use of a variableresistan-ce in-the-central grounded circuit of the high tension transformer of an X-ray tube system for the -purpose-ofstabilizing the discharge current flowing through the tube is disclosed in any United States "patent,

No. -2,319,378, granted May 18, 1943. 'In this pat ented system as long as the current Wave shape ismaintained there is alwaysafixed'relationship 'bet-ween'its average and peakvalue. If'changes in the shapeof the currentwave occ'imthis-relationship between average and peak "values 01 the current is greatly disturbed. -Many-fac'tors in the X'-ray system tend to change the shape of the current wave. The error thus introduced rrlay theoretically amount to several hundred percent.

The present invention =relates to =the iiseof a condenser in the central grounded circuit of the high potential transformer feeding an X-ray tube, for the purpose-of stabilizing the discharge current flowing through the "tube "regardless 2of the wave shape which the: current may take. The condenser is an accumulator for quantities of electricity which integrates the current-flow during each half cycle so that the peak voltage reached by the condenser represents an integration of the current flowing through the time period of the half cycle. This condenser peak '7 Claims. (Cl. 250-397) voltage is proportional to -the average value of v the feeding current regardless of the shape of the current wave.

-An object of the present invention isto provide an X-ray system wherein the milliamperage flow ing through the X-ray tube is -maintained substantially constant, regardless of changes-in the current wave shape as it appears in the central grounded circuit of the high tensiontransformer.

Another object of the present'inventionis the provision of an X-ray systemwherein-any tendency for the discharge current to vary, automatically causes a variation in thefilamentheab 'ing current, thereby maintaining the rnilli'a'mperage of the discharge current substantially constant, regardless of changes in the "wave shape of the current flowing through the tube.

Another object of the present irivention isthe provision of an X-ray system wherein current flow chargin a condenser in the excitation circuit automatically varies the current flow through the plate circuit of an amplifier tube, which in turn renders an auxiliary circuit operative-to cause a variation in the filament heating currentinverselyto the variation in the discharge current, thereby *maintaining "the latter :substam tially cohstant. H

Another object'of thepres'e'nt invention is to provide a bias on an amplifier tube cont-r01 grid in a circuit controlling the filament heating means mentioned above, together with a control circuit" subject to the discharge current through the X-ray tube Which,-When applied to'said con- =tro1-g1id, will vary "its -bias, if necessary, to hold said discharge *current-at'a desired value.

I Still another object "of the present invention comprises the circuits defined in the receding paragraph wherein said control circuit is precharged to provide substantially the -normal-expact-ea bias on said control grid together with means for removing said normal bias froursaid "control grid and applying said control circuit thereto coincident with the energiza'tion or the 'X-ray tube,-so that any slight variation from the desired value =0l the discharge "current may be immediately corrected.

-A further obj ect' of the present invention is the provision 0f means for selecting the 't'iiilliaine perages desired for an X-ray tube exposure which at the -*sa'1'ne time "Will select a suitable control condenser for connection in theeen tral grounded circuit of the high tension transformer if necessary a suitable variable "compensating volt, age in the control circuit mentioned in the preceding paragraph Which goiIe-rns the bias oh the control grid of the amplifier tube. Thus, auto matically all of the fa'c'tors areselectedwhich are necessary fOi maintai l1iI'1g 'the "desired discharge currentthr'ough the tube at the moment the tube is energized Ether obj ects and advaiitagesof the present in vntioh Willb apparent to those skilled in the art and the essential fea'tu'res thereof willbe-s'e't forth ih the appended claims. 7 1

In the drawings, the "sole figure is a diagram inati'c illustration :Of a stabilizer system uti-liih'g my invention. I

"In the drawing I have i llustrateden X-ray tube 'N! having an aiiode H and a cathodec'r filament t2 Which-are energized throiigh line's M3 and through a brid eqectifier t Which-in turn is supplied with current :ir'om a h potential transformer it. The transformer 'as 'alpriraary 43a and a secdndary 46b which -a ceritral grounded circuit which there is provided a milliameter =1! and one :or more control can densers 18a, Hib and [80, as will presently appear, Preferably, a contactor'switch ii; for ini tiating an X-ray exposure is in series with the transformer primary Ilia. This contactor switch is controlled by relay which is energized from the source L3, L4 when the exposure button 2| is depressed. A relay 22 is provided in parallel with the relay 20 for a purpose which will later appear. When the X-ray tube is energized current flow appears in the central grounded circuit containing the condenser l8a. It is a purpose of the present invention to utilize the peak voltage of this control condenser to stabilize the current flowing through the X-ray tube.

The alternating current flowing charging the control condenser [8a is fed by lines 23 and 24 through a rectifier 25 and therectified current flows through lines 26 and 21 to the seconda y condenser 28. The peak voltage built up on the condenser 28 will be proportional to the average value of the alternating current charging condenser lBa no matter what the shape of the current wave. The potential built up on the condenser 28 is fed through lines 28 and 29, compensating voltage 38a, 3022 or 300, and lines 3| and 32 to the cathode 33 of the amplifier tube 34. The control grid 35 of the amplifier tube is provided with a suitable bias through the variable resistor 36 and lines 31, 38, contacts 39 and line 40. The screen grid 4| of the amplifier tube is provided with a suitable bias through line 42 and resistance 43. The circuit through plate 44 of the amplifier tube includes line 45, the D. C. winding 46 of a saturable reactor 41, line 48, condenser 49 and line 50. Tube 34 thus provides amodulator device for varying the heating effect of filament l2 responsive to variations in the peak voltage of condenser 28.-

The relationship in the control circuit for amplifier tube 34 is related to the normal expected voltage on condenser 28 corresponding to the desired current flow charging the control condenser IBa. The compensating voltage shown at 30a, 30b or 300 is arranged to buck the potential of condenser 28 and the relationship is such that the potential of condenser 28 minus the compensating voltage equals the bias on the control grid 35.

Any suitable means may be provided for providing the necessary circuits for amplifier tube 34 including the plate voltage, grid bias, compensation voltage and screen grid voltage. The means shown comprises a transformer 5| having a primary 5hr supplied from a suitable source L5, L6. The main secondary Winding of this transformer 51b is connected through a rectifier 52 so as to provide rectified current through lines 53 and 54 to lines and 48 respectively. The smoothing condenser 49 performs its usual function. A secondary winding 55 may be provided for heating the cathode of the rectifier tube 52. Another secondary winding 56 may heat the cathode for amplifier tube 34 and other windings 51 are provided for the rectifier 25. The proper connections from the windings 56 and 51 are omitted for clearness. Preferably, a voltage regulator tube 58 of the VR150 type provides stabilized voltage for the compensated voltage windings and for the screen grid. Preferably, also a voltage regulator tube 59 of the VR75 type provides stabilized voltage for the control grid bias.

Means is provided for varying the heating current for filament l2 responsive to changes in the plate circuit of tube 34. Many devices might be used, but I have chosen the saturable reactor 41. It is well known that the passing of a direct current through the winding 43 of this reactor has a considerable controlling influence on the alternating current flowing through the windings 60 of this reactor. For a very low D. C. magnetization of the core of the reactor, the impedance is at a maximum. For full D. C. saturation of the core, the impedance is at a minimum. The A. C. windings of the reactor (of which a plurality may be provided as shown) are connected by selector switch BI and lines 62 and 63 in series with the primary winding 34a of a transformer 64 whose secondary winding 64!) is connected by lines 65 and 66 with the X-ray tube filament I2.

Referring back to the relay 22 previously mentioned, it will be noted that besides the pair of normally closed contacts 39 influenced by this relay, there is also a pair of normally open contacts 39a. It results from this construction that when the button 21 is depressed for an X-ray exposure, relay 22 is energized causing contacts 39 to open and causing contacts 39a to close. The opening of contacts 39 removes the normal bias from the control grid 35 of the amplifier tube 34. At the same time this grid is connected by line 40, contacts 3% and lines 6! and 21 with the negative side of condenser 28. If the desired current is flowing in the central secondary circuit and charging the condenser 18a then the normal expected potential will be developed in the condenser 28. This voltage minus the bucking voltage provided at the compensating voltage 30a will then equal the normal bias on the grid 35. Thus, there will be no change in the bias of grid 35, there will therefore be no change in the current flowing in the plate circuit and there will be no change in the filament heating current.

Under conditions similar to those of the preceding paragraph, if the contactor is closed for an exposure and the X-ray tube current is too high, then the condenser 28 will be charged above the normal expected potential and when the compensating voltage is deducted from this amount it leaves a greater negative bias upon the control grid 35. This decreases the plate voltage and therefore the direct current flowing in the winding 46 of the saturable reactor 4'1. This increases the impedance of the A. C. windings Bi) and decreases the current in the A. C. circuit feeding the filament transformer primary. This cuts down the'current in the filament transformer secondary 64b so that the heating effect of the filament I2 is cut down until the current flowing in the X-ray tube is that desired. I Under similar conditions if the contactor is closed for an X-ray exposure and the X-ray tube current is too low, then the condenser 28 is charged below the normal expected potential and when the compensating voltage is deducted from this potential it leaves a bias on grid 35 which is more positive than normal. This will increase the plate current and therefore the direct current in the winding 46 of the saturable reactor 41. This decreases the impedance of the A. C. windings 53 and increases the current in the A. C. circuit feeding the filament transformer. Therefore the filament current will increase until the tube load comes up to that normal or desirable amount. 7

In order to shorten the time necessary to fully charge condenser 28 to the potential necessary to compare with the normal desired potential, I may provide a second pair of normally closed contacts 68 under the influence of relay 22. These contacts are normally closed and by means of lines 69 and Ill complete a circuit which connects the condenser 28 to the control grid bias and the weenie .5 compensating voltage so that condenser 28 is charged to the-expected normal potential-prior to the moment *an exposure is initiated. At such time-relay -22 is energized coincidentally with relay 20 and contacts 88 are-opened atthe-same time that contacts 3911 are closed for the purpose previously mentioned.

"In case the voltage on the condenser 28 needs to "be slightly lowered, a bleeder resistor H is *provided which is connected across condenser *28 by lines 72 and i3 and contacts 680i when rela} 2'2 is-energized. The resistor 'i-i is-so-dimensioned that the discharge is not greater than ten per cent-of thecondenser charge for one half "cycle.

By properly selecting the condenser -l=8a and the peak voltage to which the condenser 28 is charged, suitable conditions may =be selected corresponding to variousdes'ired current fiowsfin the central secondary grounded circuit of the trans- 'form'er it. -In one case utilize a condenser 18a of one-quarter microfarad, and a currentof five milliamperes flowing in the central "secondary grounded circuit wil charge the condenser 28 upto a peak voltage oi'eighty-th-ree volts. Under these circumstances I use a compensating voltage 30a of seventy-one volts and a bias on the grid 35 of twelve volts. If the condenser [8b is 1 m. f. d., I may provide a switch 14 having a .contactor 14a adapted :to-connect condensers [8a and l8b simultaneously giving a capacity of one and one-quarter m. f. d. Ifnow the condenser 28 is charged to a peak of eighty-three volts this will correspond to a current fiow of twenty-five m. a. 'in the central secondary grounded circuit.

=Iunder the .sameconditions, the condenserizs is charged to a .peak voltage o'fone hundred and sixty-six volts this .will correspond to a tubecurrent of fifty m. .a. This may -be arranged by changing the compensating voltage 33b to one hundred "and fifty-.Iour volts .utilizing :a @contact arm 16 which is a portion of a selector 19 which may be connected with the switch 14 by means indicated diagrammatically at 18. Thus, a monitor control might be arranged simply to be set at twenty-five in. a. by turning the switch 14 to connect the buttons A and B together while at the same time selecting seventy-one volts on the variable compensating voltage 3%. In similar manner, fifty m. a. might be selected by setting the compensating voltage 39b for one hundred and fifty-four volts. If the condenser |8c were of four m. f. d. capacity then the switch contactor Ma might be turned to connect the buttons B and C simultaneously giving a total capacity in the condensers l8b and I80 of five m. f. d. This would correspond to a tube current of one hundred m. a. when the condenser 28 is charged to a peak voltage of eighty-three volts. By means of suitable arrangements the contact arm 16 may be arranged to select a compensating voltage at 380 of either seventy-one volts or one hundred and fifty-four volts as previously explained in connection with 301). In case one hundred and fifty-four volts is selected then condenser 28 may be charged to a peak voltage of one hundred and sixty-six volts which will correspond to a tube current of two hundred m. a. These figures are representative only and illustrate how by a proper selection of the condenser 18a and lBb or 80 and the proper compensating voltage, various desired tube currents may be automatically selected.

The purpose of arm 1'! and contacts 11a is to insure the connection of the resistor 30a, 30b or 300, selected b arm '16, in :circuit from il-ine fl through resistors-'81! and 8 i and line ti' to t me 3]. 'The voltage regulator tube fl insures com 's'tant voltage across =re'sistors t'fia, ifflb or flc. 'whatIclai-mis: I '1. The combination o'f an X ray tubeprovi'ded with a heated filament, means for heating-said filament, an energizing circuit 'for "said *tub'e ineluding a high tension transformer having'ase'c 'om'iary vi ith a central grounded circuit, the critput "of said secondary being electrically connected with the anode and cathode of said tuba-a con trol condenser in said central grounded means for rectifying current charging said condenser, -a secondary condenser -elec'trically -connected to receive said rectified current and tob'e charged thereby, an amplifier tube having a plate and a cathode and a control grid, anormally open comparison circuit including said secondary condenser and said amplifier "cathode and "said' grid, normal potential for said secondary condenser corresponding to the desired current fiowthrough said control *condenser in said central grounded circuit, means in said comparison circuit'forapplying -a compensating voltage bucking said-normal potential -of said secondary condenser, means for applying a bias to said control grid "equal-to said normal potential minus said compensating voltage, a plate-circuit-inoludingsaid plate 'of'said amplifier tube, means in said plate circuit Tor controlling said filament heating means "responsive to current flow in said plate circuit, and means for-disconnecting said-bias applying means and for closing saidcomparison circuit coincident with energization of said X-ray tube, whereby variations in said normal potential duetoundesired flow in said central grounded "circuit will vary the bias on said control grid and vary the current flow in said plate circuit, saidmean's "in said plate circuit forcontrolling 'sai'd filament heating means being electrically responsive to increased or-decreased current iiow in said plate circuit to increase or decrease respec'tively the efiect of said heating means.

2. The combination of an X-ray tube provided with a heated filament, means for heating said filament, an energizing circuit for said tube including a high tension transformer having a secondary with a central grounded circuit, the out put of said secondary being electrically connected with the anode and cathode of said tube, a condenser in said central grounded circuit, means for rectifying current charging said condenser, a secondary condenser elecrtically connected to receive said rectified current and to be charged thereby, normal potential for said secondary condenser corresponding to the desired current flow through said first named condenser, means normally charging said secondary condenser substantially to said normal potential, and circuit means efiective only when said X-ray tube is energized and electrically associated with said secondary condenser and with said filament heating means for increasing and decreasing the effect of the latter responsive to decrease and increase respectively in potential across said first named condenser.

3. The combination of claim 1 including a plurality of said control condensers, a plurality of said compensating voltage applying means, and common means for selecting a desired control condenser and a desired compensating voltage applying means. 7

4. The combination of an X-ray tube provided with a heated filament, an energizing circuit for said tube, heating means for said filament, a control device for said heating means, a condenser connected to said energizing circuit so as to build up a peak voltage in said condenser in response to discharge current through said tube, and a modulator device having a control element in circuit with said condenser and varying with the peak voltage of the latter, said modulator device having a controlled element in circuit with said control device for decreasing and increasing the heating of said filament responsive to increase and decrease respectively of the peak voltage of said condenser.

5. The combination of an X-ray tube provided with a heated filament, means for heating said filament, a control device for said heating means,

anenergizing circuit for said tube, means in said tube circuit for electrically integrating the current flowing therein during successive half waves,

and a modulator device having a control element in circuit with said integrating means and varying with the peak voltage of the latter, said modulator device having a controlled element in circuit with said control device for decreasing and increasing the heating of said filament responsive to increase and decrease respectively of the peak voltage of said integrating means. a

6. The combination of an X-ray tube provided with a heated filament, an energizing circuit for said tube, heating means for said filament, a control device for said heating means, a condenser having electrical connections with said tube for subjecting said condenser to a peak voltage charge which is an integration of successive current waves in said tube circuit, a space discharge tube having a filament and aplate and a control grid, an electrical connection between said condenser and said control grid, and a plate circuit including said plate and said control device for said filament heating means for increasing and decreasing said filament heating means responsive to increase and decrease in current in said-plate circuit.

'7. The combination of an X-ray tube provided with a heated filament, an energizing circuit for said tube, heating means for said filament, a control device for said heating means, a condenser having electrical connections with said tube for subjecting said condenser to a peak voltage charge which is an integration of successive current waves in said tube circuit, electrical means for applying a predetermined desirable potential to said condenser independent of said peak voltage, a space discharge device having a control grid and a filament and a plate, switch means normally connecting said electrical means with said grid for applying said predetermined potential thereto, control means operable concurrently with energization of said X-ray tube for disconnecting said switch means normal connection and for applying said peak voltage to said control grid, and an electrical circuit including said plate and said filament heating means control device for increasing and decreasing said filament heating means responsive to increase and decrease respectively of current in said electrical circuit including said plate, whereby to hold the current flowing in said X-ray tube substantially constant.

LOUIS L. WEISGLASS,

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,961,703 Morrison June 5, 1934 2,167,529 Scaife July 25, 1939 2,236,195 McKesson Mar. 25, 1941 2,319,378 Weisglass May 18, 1943 2,339,902 Akers et a1 Jan. 25, 1944 2,384,647 Schwarzschild Sept. 11, 1945 2,408,091 Olesen Sept. 24, 1946 

